This invention relates generally to solid ink forms, and more particularly to solid ink pastilles for use in high-speed solid ink jet printers.
In general, phase change ink image producing machines or printers employ phase change inks that are in the solid phase at ambient temperature, but exist in the molten or melted liquid phase (and can be ejected as drops or jets) at the elevated operating temperature of the machine or printer. At such an elevated operating temperature, droplets or jets of the molten or liquid phase change ink are ejected from a printhead device of the printer onto a printing media. Such ejection can be directly onto a final image receiving substrate, or indirectly onto an imaging member before transfer from it to the final image receiving media. In any case, when the ink droplets contact the surface of the printing media, they quickly solidify to create an image in the form of a predetermined pattern of solidified ink drops.
An example of such a phase change ink image producing machine or printer, and the process for producing images therewith onto image receiving sheets is disclosed in U.S. Pat. No. 5,372,852 issued Dec. 13, 1994 to Titterington et al. As disclosed therein, the phase change ink printing process includes raising the temperature of a solid form of the phase change ink so as to melt it and form a molten liquid phase change ink. It also includes applying droplets of the phase change ink in a liquid form onto an imaging surface in a pattern using a device such as an ink jet printhead. The process then includes solidifying the phase change ink droplets on the imaging surface, transferring them the image receiving substrate, and fixing the phase change ink to the substrate.
As is well known in the art, phase change inks used in such machines are waxy, melt at less than about 120.degree. C., and therefore are very different from dry powder toners that are used in xerographic machines. Examples of such phase change inks are disclosed in the following references. U.S. Pat. No. 6,319,310 issued Nov. 20, 2001 and entitled “Phase Change Ink Compositions” discloses a phase change ink comprising (a) a carbamate or thiourea, said carbamate or thiourea having a melting point of no higher than about 120.degree. C. and an acoustic loss value of no more than about 100 decibels per millimeter, (b) a colorant, (c) a branched hydrocarbon with a number average molecular weight of no more than about 10,000 and a melting point or softening point of no more than about 120.degree. C., (d) an optional plasticizer, (e) an optional alcohol having a melting point of less than about 90.degree. C. and an acoustic loss value of no more than about 100 decibels per millimeter, (f) an optional lightfastness-imparting agent, and (g) an optional antioxidant.
U.S. Pat. No. 6,096,125 issued Aug. 1, 2000 and entitled “Ink Compositions” discloses an ink composition comprised of (1) a mixture comprised of a salt and an oxyalkylene compound wherein the conductive mixture possesses a melting point of from about 60.degree. C. to about 120.degree. C.; (2) an ink vehicle compound with a melting point of from about 80.degree. C. to about 100.degree. C.; (3) a viscosity modifying amide compound; (4) a lightfastness component; (5) a lightfastness antioxidant; and (6) a colorant.
Conventionally, the solid form of such solid or phase change inks is a “stick”, “block”, “bar” or “pellet” as disclosed for example in U.S. Pat. No. 4,636,803 as illustrated in FIG. 4 as a bullet shaped or cylindrical pellet 424 that is engaged at its rear side by a turn in a helix 442. In U.S. Pat. No. 4,739,339 the solid ink is shown as a cylindrical block; in U.S. Pat. No. 5,038,157 as a hexagonal bar; and in U.S. Pat. No. 6,053,608, as illustrated in FIG. 3, it is shown as a tapered block 300 with a stepped configuration having a length L1 of 16.7 mm, a width L2 of approximately 13 mm, and a height H! of about 15.6 mm. Further examples of such solid forms are also disclosed in design patents such as U.S. Design Pat. No. D453,787 issued Feb. 19, 2002. In use, each such block form “stick”, “block”, “bar” or “pellet” is fed along a channel in the machine frame into a heated melting device that melts or phase changes the “stick”, “block”, “bar” or “pellet” directly into a print head reservoir for printing as described above.
Additionally as illustrated in FIG. 5, it is further merely suggested in U.S. Pat. No. 4,636,803 that the solid ink therein can be provided and handled in granular form or as granules that according to the Wentworth-Udden particle sizing scale will have a size of 2 mm to 4 mm. As shown in this patent, a substantially cylindrical housing 532 receives an auger 542 that is rotated by a motor 548. Interstices between the cylindrical housing 532 and a surface of the auger 542 are filled with the solid-state ink in granular form 524. As the auger 542 rotates, the ink 524 in granular form approaches a discharge location 536 and falls through the discharge opening 538 into a trough 540.
Nevertheless, primary difficulties with such solid forms of phase change inks still include undesirable electrostatic charging, clogging, jamming, and a relatively low melt rate. Consequently, conventional phase change ink image producing machines or printers, particularly color image producing such machines or printers, are low throughput machines, typically producing at a rate of less than 30 prints per minute (PPM) and ordinarily cannot approach, let alone exceed 50 prints per minute.
In accordance with the present disclosure, there is provided a particulate composition of solid phase change ink is comprised of sub-granular size pastilles composed of at least a salt, an ink vehicle compound, a viscosity modifying amide compound and a colorant, and each sub-granular size pastille of the particulate composition is at most the size of very coarse sand, and has a diameter of at most 2 mm on the Wentworth-Udden particle-sizing scale for increasing a melting rate thereof at a melting temperature of the solid phase change ink.